A radome is a thin shell of uniform thickness which is normally used to house and protect an antenna from the weather. Because of the interposition of the radome between the antenna and outside space from which the antenna is to receive or transmit signals, the radome always adds some refraction and insertion losses to the signal and, as a consequence, the radome has heretofore been regarded as hinderance to the radiation performance of the antenna.
A further problem with which the present invention is concerned relates to the number of antennas which are employed to cover the whole spherical sky, and, particularly, with minimizing the number of antennas required for this purpose. Assuming that each antenna is mounted on an altitude-azimuth mount or its equivalent, the scanning area of each antenna is a circular region. The term --circular region-- is referable to a --small circle-- which, in the terminology of spherical trigonometry, is the intersection of a sphere and a plane cutting the sphere.
The largest circular region is the spherical sky itself. It is not possible for a single antenna to scan the entire sky because of blockage by the antenna mount. The next largest region, then, is a hemispherical region. Two antennas, with their broadside directions pointing in opposite directions, are required to scan the entire sky, provided that each antenna is capable of scanning up to 90.degree. from the broadside direction. However, if such antennas are not available, it can be shown that four antennas would be required to cover the entire sky without holes with their broadside directions being the normals of the surfaces of an equilateral tetrahedron. In that case, the scanning angle required from each antenna must range between 0.degree. to 70.5.degree., which is not significantly reduced from the 90.degree. required for a two antenna configuration. Thus, it is clearly highly desirable to provide a radome-lens comprising: a shell of dielectric material having an outer surface in the form of a small circle defined by a sphere and a plane intersecting said sphere, an opening at one end of the shell for reception of an antenna therein, the surface having a central axis which is normal to the plane and extends through the center of the sphere, and an inner surface having a spherical portion centered at a second center disposed along the axis between the first mentioned center and the outer surface and including a plurality of zones extending toward the opening and concentrically disposed along the axis, each zone being centered at the second center, adjacent zones being separated by a frusto-conical surface which converges at the second center, the radial height, h, of each frusto-conical surface being given by ##EQU1## wherein .lambda..sub.o is the designed wavelength of the incident or transmitted wave, and .epsilon..sub.r is the relative permittivity of the lens.
When so constructed, the present invention functions as a radome in the sense that it houses and protects an antenna in the usual manner. It also functions as a lens in the sense that it amplifies the scan angle of the antenna from an angle of less than 90.degree.to 90.degree. or more without much spherical aberration. Such amplification avoids ground lane obstruction and, accordingly, only two antennas, each equipped with the radome-lens of the present invention are required to cover the whole sky. In an aperture planar phased array with electronic scanning, such amplification enables the array to retain substantial antenna gain and partial dual polarization capability.
The aperture could be a microstrip antenna array scanned completely electronically or a reflector scanned completely mechanically, or other hybrid systems of microstrip antennas and reflectors with partial electronic and partial mechanical scanning.
Also in accordance with the invention there is provided a radome-lens for housing an antenna and amplifying transmitted or received rays, comprising: a shell of dielectric material, said shell having an outer surface, at least a portion of said outer surface being in the form of a small circle defined by a sphere and a plane intersecting said sphere, said outer surface defining a central axis normal to said plane and extending through the center of said sphere, an opening at one end of said shell for reception of an antenna therein, and an inner surface having a spherical cap portion at the end of said inner surface remote from said opening and a plurality of zones extending from said cap toward said opening, said cap and each said zone being concentrically disposed about said axis and centered at a second center, said second center lying on said central axis between said first mentioned center and said outer surface, and said zones being disposed between said second center and said cap, the radius of each said zone being larger by a predetermined amount than its adjacent zone remote from said opening, and said cap and each said zone being separated from its adjacent zones by a frusto-conical surface which converges at said second center, the radial height, h, of each said frusto-conical surface being given by: ##EQU2## where .lambda..sub.o is the design wavelength of the incident or transmitted wave, and .epsilon..sub.r is the relative permittivity of the lens.
Further in accordance with the invention there is provided a radome-lens for housing an antenna and amplifying transmitted or received rays, comprising: a shell of dielectric material, said shell having an outer surface, at least a portion of said outer surface being in the form of a small circle defined by a sphere and a plane intersecting said sphere, said outer surface defining a central axis normal to said plane and extending through the center of said sphere, an opening at one end of said shell for reception of an antenna therein, and an inner surface having a spherical cap portion at the end of said inner surface remote from said opening and a plurality of zones extending from said cap toward said opening, said cap and each said zone being concentrically disposed about said axis and centered at a second center, said second center lying on said central axis between said first mentioned center and said outer surface, and said zones being disposed between said second center and said cap, the radius of each said zone being larger by a predetermined amount than its adjacent zone remote from said opening, and said cap and each said zone being separated from its adjacent zones by a frusto-conical surface which converges at said second center, said radome-lens being adapted for reception or transmission of frequencies f.sub.1 and f.sub.2 wherein f.sub.2 is almost twice f.sub.1, i.e., EQU f.sub.2 =2f.sub.1 +.DELTA.f
and the radial height, h, of each said frusto-conical surface being given by: ##EQU3## wherein c=speed of light, .epsilon..sub.r =the relative permittivity of said lens.